This project examines the effects of intermittent (2/hd, 5/d wk) exposures to O3 and H2SO4 upon clearance defense mechanisms of the lung, using the rabbit as the animal model. Tracheobronchial mucociliary clearance, alveolar clearance and functional properties of macrophages obtained by lavage from exposed animals will be assessed. In addition, permeability of bronchila mucosa and alveolar epithelium will be examined, as will histology of lung tissue at selected times during the exposure series. Exposures will last up to 12 mo., with groups of rabbits sacrificed at 4, 8, 12 and 15 mo. The latter provides for a recovery period to examine resolution of effects. Clearance is studied in unsedated animals using radioactively tagged tracer aerosols. The results of this project will help in elucidation of the role that alteration in clearance function may have in pathogenesis of chronic lung disease, and the temporal relationship between changes in a number of factors which could affect defense functions.